(1) Field of the Invention
This invention relates to the rotary-file dental treatment devices.
(2). Description of Related Art
Currently, the dental treatment devices that use rotary files, such as the nickel-titanium files of different diameters based on the dental work to be done, in root canals have means for measuring torque and/or means for measuring root canal length to limit the breaking of files and/or to stop the rotation of the file in the apical region, but have few if any safety means for avoiding the breaking of files, for monitoring the precision of the stopping of the file in the apical region or else for keeping dental debris from being projected into or under the apical region.
For reasons of stability of measuring or design, regardless of the measuring means, the measuring of the root canal position of the file is an averaged and smoothed measurement that makes it possible to eliminate outliers or speed fluctuations of the file.
Such a smoothed measurement does not at any moment provide the exact position of the file, whereby a sometimes significant delay is noted on the measurement of position of the file.
This is all the more significant provided that the practitioner is to apply a back-and-forth movement to bring out the dental sludge and provided that the speed of insertion of the files in the tooth is not controlled.
This situation brings about a non-negligible source of error on the depth reached by the file in the canal with regard to a precise setting of the depth to be reached.
The documents U.S. Pat. No. 5,902,105 and U.S. Pat. No. 5,980,248 describe dental treatment devices that comprise means that are suitable for gradually slowing the speed of rotation of a motor driving the file before the stopping thereof so that the work of the file decreases with the lowering of the speed of rotation of the motor.
One drawback of this method is that when the motor slows down, the file no longer works normally and in particular can be caused to work by torsion impacts, which fatigues the file and reduces its reliability.
In addition, when the file is in the apical region, a slowing of the file can cause a screwing of the file into the tooth, which carries with it the risk of piercing the conduit, with debris being projected under the apex, source of infection, or breaking the file.
A known process for stopping the motor consists in measuring the current drawn by the motor at the terminals of a resistor inserted into the power circuit, amplifying and integrating this signal, then converting it by means of an analog/digital converter so as to compare the result of the conversion to a value that represents a given torque limit before acting on the control integrator and electrically stopping the motor in its motion.
According to this process, the motor will stop only when the torque that is braking has overcome the inertia of the kinematic and logical unit.
This process has the additional drawback that the delays that are introduced by the measuring chain repel the desired stopping action by a non-negligible period of time that can produce the fracturing or the breaking of the file in the tooth.
To avoid the screwing of the file, it was also provided in the document U.S. Pat. No. 5,980,248 to rotate the file backwards at high speed after the apical stop. Such a device has the drawback of sending dental debris back into the apex, which is a source of contamination of the dental cavity.
For its part, the document EP 0 966 237 describes a process and a device for measuring in real time the distance between the distal end of an electrode that is inserted in the radicular canal of a tooth and the apex of said canal and the location of the apex of a tooth.